[I, Ipr, Tf] ~ (about/on/upon sth) form opinions without having definite or complete knowledge or evidence; guess 思考; 思索; 推断; 推测: speculate about/upon the future 对未来的推想 * I wouldn't like to speculate on the reasons for her resignation. 我不愿意猜测她辞职的原因. * I can only speculate that he left willingly. 我看他一定是自愿走的. 
[I, Ipr] ~ (in sth) buy and sell goods or stocks and shares in the hope of making a profit through changes in their value, but with the risk of losing money 投机; 做投机买卖: speculate in oil shares 做石油股票的投机买卖 * speculating on the stock market 进行证券投机.> speculator n person who speculates (speculate 2) 投机者; 投机商.